Tap-changing transformer system



April L J. HIBBARD ET AL 2,467,747

TAP-CHANGING TRANSFORMER SYSTEM Filed June 25, 1945 5 A? g zl 29 a Z f7uxPa/h when 4 g 33 on/y o /'5 .fhoff60. 3 H 6. 0 I iUlUl L F7ux Raf/7 when r /ux/ a/h when 320 093 34 3Z0na 33 are \shorfed are ewe/fed WITNESSES: INVENTORS ATTO EY Patented Apr. 19, 1949 TAP-CHANGING TRANSFORMER SYSTEM Lloyd J. Hibbard, Pittsburgh, and Jesse B. Gibbs and Roy L. Brown, Sharon, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 25, 1945, Serial No. 601,410

7 Claims. 1

Our invention relates, generally, to control systerns and, more particularly, to systems for controlling the operation of electric locomotives and similar vehicles.

On most of the alternating-current electric locomotives in operation in this country the required voltage is supplied to the traction motors 'by changing taps on the secondary winding of the power transformer. This may be objectionable on large locomotives because of the large amount of current that must be conducted by the tap-changing switches.

In Europe some locomotives have been provided with control systems in which the tap-changing switches are connected to the high voltage primary winding of the power transformer, thereby decreasing the required current capacity of the switches. However, the European systems have certain disadvantages, such as the size and weight of the transformers and switching apparatus, and an object of our invention is to gain the advantage of high-tension notching with simpler and lighter apparatus than that used in Europe.

Another object of our invention is to secure a relatively large number of accelerating steps or notches with a relatively small number of taps on a transformer.

A further object of our invention is to provide an accelerating system in which the voltage steps in the lower range are smaller than those in the upper range.

Other objects of our invention will be explained fully hereinafter or will be apparent to those skilled in the art.

In accordance with one embodiment of our invention, the transformer for a locomotive comprises three sets of windings mounted on a common core. Each set comprises a primary winding and a secondary winding. The secondary windings' are connected in series-circuit relation across the traction motors and the primary winding of one set is utilized as an autotransiorrner and is provided with a plurality of taps which are connected to the other primary windings by tapchanging switches operable in sequential relation. The other two primary windings are made in two equal parts which are symmetrically connected to the two ends of the autotransformer during the tap-changing operation.

For a fuller understanding of the nature and objects of our invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a schematic diagram of a control system embodying our invention;

Fig. 2 is a chart showing the sequence of operation of the switches illustrated in Fig. 1;

Figs. 3 to 6, inclusive, are diagrammatic views showing the distribution of the flux in the transformer core for difierent conditions of operation; and

Fig. '7 is a View of the transformer core.

Referring now to the drawing, the system shown therein comprises a plurality of motors 25, which may be connected in parallel-circuit relation across power conductors 26 and 21 by means of switches Ll to LB, inclusive, and a power transformer T having three sets of windings 3|, 32 and 33 disposed on a common core 30, as shown in Fig. 3. The set of windings 3| comprises a primary winding Al and a secondary winding A. The set of windings 32 comprises primary windings BI and B2 and a secondary winding B. The set or windings 33 comprises primary windings Cl and C2 and a secondary winding C. The secondary windings A, B, and C are connected in series-circuit relation and supply current to the motors 25. The polarity of the windings may be so determined that the direction of flux under various conditions is as shown in Figs. 4, 5 and 6.

The primary winding Al is connected between a pantograph current collector 28 and ground. The collector 28 engages a trolley conductor 29 which may be energized from any suitable source of alternating-current power (not shown). If desired, another secondary winding (not shown) may be added to the windings 3| and utilized for supplying power for operating auxiliary equipment on a locomotive such as blowers and air compressors.

The primary winding Al is provided with a plurality of taps in order that it may be utilized as an autotransformer to excite the primary windings Bl, B2 and Cl, C2. A plurality of tapchanging switches l to 5, inclusive, and Hi to 20, inclusive, are provided for connecting the transformer taps to the primary windings Bl, B2 and CI, C2. The tap-changing switches l to 5 are connected to the primary windings BI and Cl through a preventive coil 34 and a double-throw switch 23. The tap-changing switches IE to 20, inclusive, are connected to the primary windings B2 and C2 through a preventive coil 35 and a double-throw switch 24.

As will be more fully described hereinafter, the tap-changing switches may be operated in sequential relation to adjust the voltage of the primary windings Bl, B2 and Cl, C2, thereby causing the secondary windings B and C to provide a variable voltage for the motors 25, to ac celerate the motors. The secondary winding A provides a fixed voltage for the motors 25 during the accelerating cycle. Double-throw switches iii and H are provided-for balancing the voltage across the preventive coil 3d during the tap.- changing operation. Likewise, double-throw switches 2i and 22 are provided for balancing the voltage across the preventive coil 35 during the tap-changing operation;

In order that the functioning of. the foregoing apparatus may be moreclearly understood, the operation of the systemwill nowbe described in more detail. As indicated by the sequence chart shown in Fig. 2, the motor switches Ll to L4 may be closed to connect half or the motors 25 across the power conductors 26 and 21. The tap-changing switches i and I6 may be closed and the double-throw switches II and 22 actuated to position a. The double-throw switches I and 2| are actuated to position b, and the double-throw switchesg23 and 24 are actuated to position a. When these switches are in the foregoing positions, the two ends of primary windings BI and B2 are connected to the same end of the autotransformer winding Al, and both primary windings Cl and C2 are short-c-ireuited. Therefore, the only voltage in the secondary circuit applied to the motors the fixed voltage of the secondary winding A.

7 On the next step the motor switches L to L8 are closed to connect the other half of the motors across the power conductors 26 and 2]. Following the closing of the motor-connecting switches, the tap-changing switches 1 to. 5. inelusive, and Hi to 20, inclusivaandthe voltage balancing switches In, H, l9, 2! and 122 may ,be operated in the manner indicated in the sequence chart to increase the voltage applied to the primary windings. BI and B2, step-by-step, thereby gradually increasing the motor voltage.

After the primary windings BI and B2 have been connected to the highest voltage taps .on the autotransformer winding Al, the doublerthrow switches 23 and 24 are actuated to position b to disconnect these windings from the tapchanging switches and connect them directly across the trolley and ground, thereby maintaining full voltage on the secondary winding B. At the same time, the two ends of each primary winding CI and C2 are connected to the same end of the autotransformer winding A l through the tap-changing switches.- Since there is no change in the voltage applied to the primary windings during this transition period, there is no change in the motor voltage.

After the transition period, the voltage applied to the primary windings GI and C2, is: increased .step-by-step by operating the tap-changing switches in reverse sequence, as indicated :in the chart shown in Fig. 2. In this manner the motor voltage is gradually increased until full trolley voltage is applied to all of theprima-ry' windings. thereby causing maximum voltage to be ap lied to the motors 25.

Iautotransformer winding A! is nequiredto excite only half of the primary windingsiB-I and 13?.v

CI and C2, at a time during the tap-changing operation. Therefore, the autotransformer is relatively small. The full range of operation of the tap-changing switches is used once for the primary windings BI and B2 and then again for the primary windings CI and C2, thereby saving taps on the autotransformer winding and simplitying the tap-changing mechanism and connections.

Furthermore, the voltage of the secondary winding B may be made smaller than the voltage of" the secondary winding C, thereby causing the voltage steps during the first half of the accelerating cycle to be smaller than those during the second half. In this manner smooth acceleration of the locomotive is provided during the starting period.

From the foregoing description it is apparent that we have provided a high-tension notching system which requires lighter apparatus and is simpler in operation than systems previously utilized in this and foreign countries. While the system herein described is particularly suitable for controlling the operation of electric locomotives, it is not necessarily limited to such applications.

Since numerous changes may be made in the above-described construction, and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In a control system, in combination, a transformer having a plurality of sets of windings disposed on a common core, each set comprising a primary winding and a secondary winding, the entire primary winding of one set being energized while in operation and having a plurality of taps thereon, a plurality of tapchanging switches operable in sequential relation to connect the primary windings of the other sets across said taps in a predetermined sequence tov vary the voltage of their secondary windings, and means for connecting the secondary winding of the one set in cumulative-series relation with the secondary windings of the other sets.

2. In a control system, in combination, a transformer having three sets of windings disposed on a common core, each set comprising a primary winding and a secondary winding, a plurality-of taps on the primary windin of one set, a plurality or" tap-changing switches operable in sequential relation to connect the primary windings of the other two sets to said taps in a predetermined sequence to vary the voltage of their secondary windings, preventive coils connected between the tap-changing switches and said primary windings, double-throw switches for balancing the voltage across said preventive coils during the tap-changing operation, and means for connecting the secondary winding of the one set in cumulative-series relation with the secondary windings of the other two sets.

3. In a control system, in combination, a transformer. having three sets of windings disposed on a common core, each set comprising a primary winding and a secondary'winding, a plurality-of taps on the primary winding of one set, a plurality of tap-changing switches operable in sequential relation to connect the primary windings of the other. twosets to said taps. in a predetermined sequence to vary the voltage of their secondary windings, preventive coils connected between the tap-changing switches and said primary windings, double-throw switches for balancing the voltage across said preventive coils during the tap-changin operation, and means for causing the variable voltage of the two secondary windings to be added to the fixed voltage of the one secondary winding.

4. In a control system, in combination, a transformer having a plurality of sets of windings disposed on a common core, each set comprising a primary winding and a secondary winding, the entire primary winding of one set being energized while in operation and having a plurality of taps thereon, switching means for selectively connecting the primary windings of the other sets to the primary winding of said one set, and tap-changing means for sequentially connecting said taps across the selected primary winding to vary the voltage of its secondary winding in a plurality of steps.

5. In a control system, in combination, a transformer having a plurality of sets of windings disposed on a common core, each set comprising a primary winding and a secondary winding, the entire primary winding of one set being energized while in operation and having a plurality of taps thereon, switching means for selectively connectin the primary windings of the other sets to the primary winding of said one set, tap-changing means for sequentially connecting said taps across the selected primary winding to vary the voltage of its secondary windin in a plurality of steps, and means for causing the variable voltage of one secondary Winding to be added to the fixed voltage of another secondary winding.

6. In a control system, in combination, a transformer having a plurality of sets of windings disposed on a common core, each set comprising a primary winding and a secondary winding, the entire primary winding of one set being energized while in operation and having a plurality of taps thereon, switching means selectively connecting the primary windings of the other sets to the primary winding of said one set, and tap-changing means for sequentially connecting said taps across the selected primary winding to vary the voltage of its secondary winding in a plurality of steps, said secondary windings being connected in seriescircuit relation, the voltage of one secondary winding being less than the voltage of another of said secondary windings.

'7. In a control system, in combination, a plurality of sets of transformer windings, each set comprising a primary winding and a secondary winding, the entire primary winding of one set being energized while in operation and having a plurality of taps thereon, switching means for selectively connecting the primary windings of the other sets to the primary winding of said one set, and tap-changing means for sequentially connecting said taps across the selected primary winding to vary the voltage of its secondary winding in a plurality of steps, said switching means being disposed to short-circuit certain of said primary windings during part of the tapchanging operation.

LLOYD J. HIBBARD. JESSE B. GIBBS. ROY L. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,913,130 Sealy June 6, 1933 

